The present invention relates to a process for the removal of dissolved metals from water. More particularly, the present invention relates to a novel process for efficiently removing metal ions, e.g., copper, zinc, cadmium, lead, chromium and nickel, from water, which process also includes effective regeneration of the filtration media.
Under environmental regulations, limits are placed on the types and amounts of pollutants that can be released into the environment. To limit the pollution of our waterways, various treatment systems are employed by industry to remove toxic metal ions from process waters prior to their discharge into natural waterways, municipal sewer systems, deep well injection, etc. Such water containing toxic metal ions is generally created by metallurgical processes, mine drainage and metal finishing processes. Many different treatments have been utilized in an attempt to remove the metal ions in order to meet the environmental regulations in a most cost effective and efficient manner.
Chemical precipitation of metal hydroxides is the most common way to remove such dissolved metals from water. In general practice, sufficient lime or caustic soda is added to raise the pH above 8 or 9, forming a fluffy, suspended hydroxide precipitate. After adequate settling, the metal sludge is disposed of or reclaimed. Lime is almost always used because of its low cost, and coagulants are generally added to improve the settling process. The most common coagulants for hydroxide precipitates are water-soluble organic polymers. These polymers attach to particles and cause small ones to collect together to make larger aggregates that settle more rapidly.
Chemical precipitation of metals using soda ash (sodium carbonate) is common, or sodium sulfide is also used where insoluble compounds result. More specific chemicals are sometimes employed for particular metals. Starch xanthate is a precipitant with functional groups that form several insoluble metal salts.
There are many disadvantages, however, to such a treatment utilizing chemical precipitation, such as: (1) the precipitate can settle slowly and incompletely, particularly if the metal ions are dilute, (2) the sludge is voluminous and contains a low percentage of solids even after long settling times, (3) the precipitate is easily redispersed by thermal agitation, such as that occurring during seasonal temperature changes in settling ponds, and (4) the metals are readily redissolved if the precipitate is contacted with slightly acidic water. Accordingly, other processes have been applied for metals removal, including reverse osmosis, ion exchange, activated-carbon adsorption, cementation, and extraction.
The use of MgO for metal ion removal from water has been suggested. For example, in the article "Mineral Processing Water Treatment Using Magnesium Oxide" by Joseph E. Schiller, Daniel N. Tallman and Sanaa E. Khalafalla, Environmental Progress, May, 1984, granular deadburned periclase MgO and powdered MgO are disclosed as being appropriate in the removal of suspended solids and dissolved heavy metals. Furthermore, published patent application 6-318-710 of the Department of Interior discloses the use of granular MgO, and deadburned MgO (periclase) specifically for metal ion removal from water. Specific metal ions listed in the publication as being suitably removable include zinc, cadmium, iron, copper, lead, chromium and nickel. Published patent application 6-325-269 of the Department of the Interior discloses the use of reactive MgO powder to precipitate such metal ions from water.
While the use of granular deadburned (periclase) MgO or powdered reactive MgO has been found to be somewhat effective in the removal of metal ions, more efficient and effective treatments would greatly enhance the opportunities for meeting and exceeding environmental regulations in a cost effective manner. A process which included a truly effective method of regenerating the filtration media, to thereby prolong the useful life of the MgO used, would also be of great benefit.
Accordingly, it is an object of the present invention to provide a novel, and improved method of treating water containing metal ions.
It is another object of the present invention to provide such a method which employs granular lightburned and hardburned MgO.
Yet another object of the present invention is to provide a method for the removal of metal ions which permits greater throughput of water before the efficiency of the MgO is greatly decreased.
Still another object of the present invention is to provide a novel method of removing metal ions from water using granular lightburned and hardburned MgO which is more effective in the amount of metal ions removed.
Another object of the present invention is to provide such a method for removing metal ions from water while permitting effective, periodic regeneration of the granular lightburned and hardburned MgO.
These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto.